Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Fluorescence activated cell sorting (FACS) is a technique used in cytometry for measuring, sorting and enriching rare cells and particles, such as beads, from large heterogeneous populations. While FACS systems offer desirable multiplexing performance, they can be large and expensive and are typically operated by specially trained staff. As a result, FACS systems are used in only a relatively small number of facilities. To allow for more widespread availability, miniaturized FACS systems (often called “μFACS”) have been developed. However, there are few commercial systems to date and those that exist have limited number of both detection and sorting channels compared to traditional FACS.
In one example μFACS system, the laser excitation light shares a common path with the flowing cells. This configuration can limit the microfluidic geometry and involves specialized coatings on the channel to permit optical waveguiding. Such coatings can make the chips more costly to fabricate and may not be suitable for all biological samples. Further, this example system only allows for a single excitation wavelength, which is not desirable if more than about ten fluorescent markers are to be identified. Another example μFACS system offers more channels with up to 4 excitation lasers and 8 fluorescent channels (along with two scatter channels), but employs a cuvette such that the excitation lasers are perpendicular to the collection path. Although this approach may have the advantage that the side scatter channel could be efficiently collected, it may be desirable to use widely available, planar microfluidic chips instead of cuvettes. In addition, this approach uses a large number of detectors, such as photomultiplier tubes (PMTs).
Accordingly, there is a need for systems that are compatible with existing FACS protocols, that are in a planar geometry such as a microfluidic chip, and that can employ a number of simultaneous fluorescent markers and emission channels on the order of what is possible with traditional FACS systems.